Bioprosthetic heart valves (BHVs) are routinely used as replacements for diseased natural valves. BHVs have lower risks of thrombogenicity and superior hemodynamics, when compared to the mechanical valves. However, BHVs do not have favorable long-term durability, primarily due to early structural failure of the leaflets. Although a range of failure mechanisms have been proposed to explain observed leaflet failures, mechanical stress during valve operation plays a significant role in failure.
To date, prototype valve durability has been quantified using experimental equipment (e.g. Rowan Ash fatigue tester, Helmholtz-type accelerated durability tester) based on FDA/ANSI/AAMI/ISO durability guidelines, even though it has been shown that accelerated testing performed under current guidelines has an uncertain relationship with in-vivo conditions. Indeed, accurate assessment of valve durability in a non-contacting, timely manner is one of the most important unresolved issues in the basic research of artificial organs. Because accelerated fatigue testers cannot provide quantitative information related to dynamics of the leaflets, experimental results for BHVs must be assessed within the framework of existing experimental limitations.
Given the difficulty in quantifying the constitutive relationship for the highly nonlinear tissue leaflets in BHVs, a plausible approach that provides quantitative data essential for reliable model prediction of leaflet durability is to measure the true, three-dimensional, transient leaflet kinematics during the opening and closure of BHVs under conditions that are similar to those experienced by the human heart. Through direct measurements, the necessary response characteristics of the leaflets to physiologic pressure/flow conditions can be obtained. Furthermore, successful implementation of a non-contacting deformation measurement system can provide insight for development of a lab-based experiment capable of quantifying the constitutive response of thin non-linear membranes, such as the valve leaflet.
Thus, a need exists for a global methodology based on a non-contacting, image-based measurement method to evaluate the three-dimensional mechanical response of tissue membranes, such as the heart valve's leaflets, in response to a variety of physiologic loading conditions. In addition, it would be desirable to use digital image correlation combined with high-speed stereo imaging to measure the transient three-dimensional deformations of the tissue leaflets under a number of pulsatile flow conditions.